This invention relates to a method of rectifying a reaction product stream. In a particular aspect, this invention relates to a process for rectifying the crude production stream obtained by the vapor phase nitration of hydrocarbons.
Hass, Hodge and Vanderbilt, U.S. Pat. No. 1,967,667, disclosed a process for the production of nitroalkanes by the vapor phase nitration of hydrocarbons, e.g. propane, at elevated temperatures and pressures. The nitration reaction with propane produces the four lower nitroalkanes and numerous by-products which are difficult to separate.
According to the present process, the vapor phase nitration stream from the nitration chamber (i.e., the nitrator) is passed through a condenser which condenses most of the normally-liquid components and separates them from normally-gaseous ones, including unreacted propane. The gaseous portion passes into a water absorber where the gas is washed of water soluble components, thereby forming the absorber bottoms. These absorber bottoms contain nitroalkanes, acetaldehyde, and other oxygenated products, etc., but only a small proportion of the normally gaseous components such as propane, CO2, CO, nitrogen and nitrogen oxides. The liquid from the condenser and the absorber bottoms are then stripped by distillation of nitroalkanes, low boiling compounds and compounds of low water solubility. The recovered condensate forms a water and an oil layer, the latter consisting largely of crude nitroalkanes plus low boiling components. This mixture of crude nitroalkanes is then delivered to a heads column where the low boilers are stripped and the remaining nitroalkanes, containing 0.05 to 0.5% formaldehyde, are then fractionated to give commercial grade nitromethane, nitroethane, 1-nitropropane and 2-nitropropane.
This process has served well for many years, but severe fouling of the heads column and reboiler by a carbonaceous material of unknown origin causes considerable difficulty. Accordingly, there is a need for an improved rectification process.